1. Field of the Invention
The present invention relates to improvements in a projection display device which projects an optical image onto a screen for video display.
2. Description of the Related Art
In recent years, with the widespread use of information terminals for the home, such as personal computers, and the practical use of high-definition television, the demand has increased for displaying video images on a larger screen with higher brightness and resolution. To meet such a demand, the development of projection display devices, such as liquid crystal projectors, is accelerated at present.
A projection display device comprises: three light sources each corresponding to a respective one of a plurality of primary colors, for example, red (R), green (G) and blue (B); three liquid crystal display panels each displaying a video image corresponding to a respective one of the R, G, and B color components; an optical path which directs colored light from each of the light sources to a respective one of the liquid crystal display panels, outputs video image light modulated by the display panels and combines the video image light from the display panels; and a projection lens which projects the combined video image light onto a screen.
As it stands, there is much room to improve the details of such a projection display device. One of the improvements is to further enhance the quality of video images displayed on the screen. There is a strong demand for developing such a technique to increase the video image quality as soon as possible.
For example, Japanese Unexamined Patent Publication No. 7-222185 discloses a projection liquid crystal display device which makes it possible to adjust the color temperature of at least one of a plurality of light sources so that chromaticity can be adjusted and sufficiently bright images can be obtained. As a color temperature adjustment method, there is disclosed an example of providing a filter that lowers colored light within a given waveband. This makes it easy to increase the brightness and adjust the color temperature.
However, the display device disclosed is complex in structure because of the necessity of a special filter for color temperature adjustment as a separate part.